GaN semiconductor devices grown on high resistivity silicon or silicon carbide substrates are known. Such semiconductor devices are typically RF devices. The substrates have high resistivity to reduce microwave loss. In order to make contact to the underside of the semiconductor device small apertures are provided in the substrate and contact is made through the apertures. This significantly increases the complexity of the assembly of the device.
In addition, growth of GaN LED devices on insulating transparent substrates (for example sapphire) is also known. As the substrate is insulating connections are made to the LED from above. This complicates manufacture.